Planet Of Wonders - "The Earth"

 

What before us?

Really wondering? 🤔🤔 Let us find.

 

Humanity's fingerprint can be seen across the planet today, from the towering skyscrapers that define our modern metropolises to the pyramids and other ancient monuments of our past. Human activity also marks our sprawling open fields of agriculture and the roads that link everything together. But what would had the world looked like when humans were not there?

Many of us want to know , so, what was there before us.

Answering this is neither easy nor that hard, so let us first began with earth. Our planet is about 4.5 billion years old. Situated 150 million km away from the Sun, it has a circumference of about 30,800 km. It is almost spherical, but bulges a little at the equator and it is flattened slightly at the North and South poles.

The first living organisms on Earth are thought to have appeared roughly 4 billion years ago. They were single-celled organisms that existed for nearly 1 billion years as the most sophisticated form of life on Earth. There were, and still are, two distinct groups of such microorganisms with different biochemical characteristics. They are classified as Bacteria and Archaea. The Archaea include microbes that live and multiply under extreme conditions, such as very high temperatures and very high salinity. It is believed that the main source of energy for the first single-celled organisms was energy-containing chemical compounds that had formed through the action of ultraviolet (UV) radiation and electrical discharges in storms. However, the quantity of energy available from such sources was severely limited, and there was surely insufficient to sustain life on the scale that it exists today.

 Now do you remember  about photosynthesis ? obviously this is what we
 were taught in our EVS classes. But this photosynthesis didn’t exist from the beginning of the earth... amused ? The fact is that, first photosynthetic organisms probably evolved early around 2.5 billion years ago simplifies the story behind its existence. the evolutionary history of life and most likely used reducing agents such as hydrogen or electrons, rather than water to survive, these were single celled cyanobacteria .This development represents one of the great watersheds in biological evolution. It changed the living world forever, but the question of when oxygenic photosynthesis evolved is still unanswered.

The development of photosynthesis had far-reaching evolutionary ramifications. Among these were the fact that oxygen began to concentrate in the atmosphere, allowing life forms that relied on oxygen for their respiratory functions to emerge. Another result was that some of the atmospheric oxygen was transformed to ozone (O3), which produced a layer in the upper atmosphere. It worked as a filter here, absorbing much of the UV light from the Sun. 

Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose, developed over time, and culminated in the Cambrian Explosion about 541 million years ago. This sudden diversification of life forms produced most of the major phyla known today, and divided the Proterozoic Eon from the Cambrian Period of the Palaeozoic Era.

Pangea Breaking Apart

The Proterozoic aeon spanned from 2.5 billion years ago to 542 million years ago. In this time span, cratons grew into continents with modern sizes. It is almost probable that at the end of the Proterozoic aeon, the majority of the continental mass was unified in a position near the south pole, and that the transition to an oxygen-rich atmosphere was a critical development. Prokaryotes evolved into eukaryotes and multicellular forms of life. The Proterozoic saw a couple of severe ice ages called snowball Earths. After the last Snowball Earth about 600 Ma, the evolution of life on Earth accelerated. About 580 Ma, the Ediacaran biota formed the prelude for the Cambrian Explosion .The earliest vertebrate creatures, including the first fishes, arose during the Cambrian period. A creature that might have been the fishes' progenitor. The diversity of life forms did not increase greatly because of a series of mass extinctions that define widespread bio stratigraphic units called biomeres. After each extinction pulse, the continental shelf regions were repopulated by similar life forms that may have been evolving gradually at some other places.

Several hundred million years ago, plants (resembling algae) and fungi started growing at the edges of the water, and then out of it. The oldest fossils of land fungi and plants date to 480–460 Ma, though molecular evidence suggests the fungi may have colonized the land as early as 1000 Ma and the plants 700 Ma. Initially confined to the water's edge, mutations and variations led in increased colonization of this new habitat. The first tetrapod developed from a fish around 380 to 375 million years ago. Fins developed into limbs that the first tetrapod used to lift their heads out of the water to breathe air, and reproduction was accomplished by depositing eggs in water. Some species began to spend their adult lives on land but continued to rely on aquatic sources for egg laying; this was the origin of amphibians on Earth. About 20 million years later the amniotic egg evolved, which could be laid on land, giving a survival advantage to tetrapod embryos. Around this time dinosaurs started separating themselves from the other vertebrates ,but the most severe extinction of the period (251~250 Ma), around 230 Ma, dinosaurs split off from their reptilian ancestors. The Triassic–Jurassic extinction event at 200 Ma spared many of the dinosaurs.

Fins Developed Into Limbs

 Evolving Amphibians

The first true mammals evolved in the shadows of dinosaurs and other large archosaurs that filled the world by the late Triassic. The first mammals were very small, and were probably nocturnal to escape predation, but one more thing to be amused of , the evolution of grass brought a remarkable change to the Earth's landscape, and the new open spaces created pushed mammals to get bigger and bigger. Fossils suggest that the early forests of North America's Great Plains region began to die out approximately 21 million years ago as a result of successive cold events. There was less moisture in the air during such episodes, with much of it trapped at the poles. This not only rendered the planet colder, but also drier and more open. Grasses spread because of their propensity to dominate dry or drought-prone environments. They are able to do so because they have evolved a more effective photosynthesis technique that loses less water than many other plants.

Plants Evolving

Six million years later, the Middle Miocene Disruption began when the Antarctic ice sheets began to develop and changing ocean currents caused world temperatures to fall. As the planet cooled, grass spread quickly on these now-dry and cooler plains, as did animals that grazed on it. Grass started to expand in the Miocene, and the Miocene is where many modern- day mammals first appeared.

During these periods several  species of organisms and animals evolved but only the most fitted to the conditions of earth survived.

 

After reading about all these time periods ,most of might be feeling sleepy ,without even thinking of what we began with, that’s the question I am asking you back ,what’s next after all these so long evolutionary processes.

Admitting that this is too short to be used as your assignments, but I hope all of you have enjoyed this article ,please share ,follow and comment your feedbacks as well as the answer of the question which I asked .